Magnetic amplifier



Dec. 22, 1959 R, A RAMEY, JR 2,918,626

MAGNETIC AMPLIFIER Filed May 22. 1953 l *I l f g I l I L .l

INVENTOR ROBERT A. RAMEY JR ATTORNEYS United States Patent MAGNETIC AMPLIFIER Robert Ancel Ramey, Jr., Pittsburgh, Pa. Application May 22, 1953, Serial No. 356,921

1 Claim. (Cl. 330-8) (Granted under Title 35, US. Code (1952), sec. 266) This invention relates to magnetic amplifier circuitry and more particularly to an improvement in magnetic amplifiers of the type disclosed in my copending application Serial No. 237,813, filed July 20, 1951 now Patent No. 2,783,315.

In the magnetic amplifier disclosed in my copending application delivery of power to a load impedance from an alternating voltage source is regulated by controlling the magnetization level of a high remanence saturable core through variations of the reactive voltage developed across a winding on the core. Generally, the amplifier is operative in repetitive cycles, each cycle comprising first and second half-cycles wherein the control function is exercised in the first half-cycle and the regulated power is delivered to the load impedance in the second half cycle.

The second half-cycle of operation may be conveniently subdivided into two phases, the magnetizing period and the load current period. In the magnetizing period the voltage source is applied through a magnetizing Winding on the core which initially may be unsaturated, the winding presenting a very high reactance to the applied voltage due to the unsaturated condition of the core. Current of a value equal to the magnetizing current of the core flows through the magnetizing winding across which is developed the entire supply voltage due to complete absorption thereof in shifting the core magnetization level. Upon saturation of the core the high reactance of the winding disappears whereby the supply voltage is transferred to the load impedance with corresponding load current flow in the amplifier. Saturation of the core thereby marks the beginning of the second or load current phase of the second half-cycle. The instant at which core saturation occurs in the second half-cycle and hence, the interval during which power is supplied to the load, should be dependent only upon the condition of the core with respect to its magnetization level as set in the preceding half-cycle. If the load impedance contains capacitive reactance, the unidirectional voltage exhibited thereby during the magnetization period interferes with proper core magnetizing action, the supply voltage being rendered less effective to magnetize the core. As a result, the instant at which core saturation occurs becomes indefinite whereby the control function exercised in the first half-cycle is rendered ineffective.

The foregoing disadvantage is eifectively overcome by the amplifier of the present invention which includes an auxiliary circuit for bypassing the magnetizing current in the second half-cycle from the load impedance. The addition of the bypass circuit permits proper magnetizing action to occur regardless of the capacitive reactance characteristics of the load whereby the desired definite control function is preserved.

Accordingly, it is an object of the present invention to provide an improved magnetic amplifier.

Another object of the'present invention is to provide an improved magnetic amplifier. operationally independent Patented Dec. 22, 1959 of the capacitance characteristics of the load to be driven. Other objects and advantages of the present invention will be come apparent from the following detailed description when taken in conjunction with the drawing in which the single figure thereof represents a schematic diagram of a magnetic amplifier embracing the present invention.

Turning now to the figure, the magnetic amplifier of my invention includes a high remanence saturable magnetic core 10 which preferably is of a magnetic material that exhibits substantially rectangular hysteresis loop characteristics with saturation at low values of magnetomotive force. Deltamax, Orthonol, etc., are examples of materials having suitable characteristics. Wound on core 10 are windings 11 and 12, hereinafter referred to as the demagnetizing or reset winding, and the magnetizing or load winding respectively, the dots adjacent the ends thereof referring to winding polarity. An alternating voltage source E at terminals 13 and an alternating voltage source E at terminals 14 are respectively provided to supply to windings 11 and 12 a demagnetizing voltage and a magnetizing voltage. The magnitudes of voltages E and E, and the number of turns of windings 11 and 12 are subject to considerable design variation provided the limitation imposed by the circuit is observed, this being that over a complete cycle of amplifier operation the time-integral of voltage of winding 11 and source E in one half-cycle must be substantially equal to the time-integral of voltage of winding 12 and source B in the next half-cycle.

Generally sources E and E will be of the same frequency and phase, therefore, when the turns of windings 11 and 12 are chosen to be equal, the magnitudes of sources E and E may also be equal. In this case voltage sources E and E may conveniently be derived from a single source appropriately coupled to the windings at terminals 13 and 14 by conventional transformer connections.

As alluded to above the demagnetizing and magnetizing voltages are to be applied to windings 11 and 12 in first and second half-cycles respectively. For this purpose unilaterial impedance devices 16 and 17, which typically may be rectifiers, are connected in series with sources E and E respectively and are so poled in relation to the polarities of these voltages that in one halfcycle voltage E is applied to winding 11 and in the next half-cycle voltage E is applied to winding 12. Winding 11, demagnetizing source E and rectifier 16 form a demagnetizing or reset circuit for core 10, the circuit addi tionally including terminals 15 for coupling a directvoltage control source B or other control element in series with source E in the circuit. Control voltage E serves the function of varying the effectiveness of demagnetizing voltage E to demagnetize core 10 whereby a different degree of core 10 resetting action may be had. Hence, the magnitude of source E may be variable from zero up to the magnitude of demagnetizing voltage E Further, the polarity of control voltage E is such as to oppose voltage E during core demagnetization and therefore opposite to the polarity of rectifier 16 which also serves to prevent flow of current from the control source to the demagnetizing winding. The polarities of the various voltages illustrated in the figure illustrate the condition of the amplifier in a demagnetizing half-cycle, that is, demagnetizing source E is being applied to winding 11 through rectifier 16, opposed by voltage E While magnetizing source E is being blocked from winding 12 by rectifier 17. It will be understood, however, that sources E and E being alternating voltages will reverse in polarity in the next half-cycle thereof.

Magnetizing voltage E winding 12 and rectifier 17 form a series magnetizing circuit for core 10, the circuit additionally including a series load impedance, generally designated at 18, to which the controlled output voltage of the amplifier is to be applied. it is contemplated that in many practical applications the load impedance 18 will include capacitive reactance and resistance and accordingly may be represented, in general, by a condenser 19 and resistance 20 in parallel. To provide in the magnetizing circuit a bypass circuit path for shunting magnetizing current from load impedance 18, impedance 21, typically a resistance, is connected in parallel with impedance 18 and rectifier 17 in series. As thus connected, the desired magnetizing action is effected through the circuit path including magnetizing source E winding 12 and resistance 21, this circuit path being independent of unidirectional voltages exhibited by the load impedance. It is to benoted tl at resistance 21 also parallels rectifier 17 which serves the additional function of preventing development of such unidirectional voltages across the bypass resistance. inasmuch as resistance 21 parallels the load impedance, in order to prevent excessive power dissipation the value of this resistance should be as high as possible without approaching the absolute magnitude of the reactance of winding 32 when core i9 is unsaturated. As the rcactance of Winding 12 may be very high, dcpendin in part upon the core material selected, resistance 21 generally will be considerably greater than the impedance of load 18 whereby a high operational efficiency is maintained.

Since resistance 21 bypasses rectifier 17, to preserve the alternate operation alluded to, an additional rectifier 22 is provided in the bypass circuit path in series with resistance 21. The polarity of rectifier 22 is consistent with the polarity of rectifier 17 whereby the application of voltage source E to winding 12 is limited to magnetizing half-cycles.

In operation of the amplifier, assuming core 18 is at the saturation lever at the beginning of a reset half-cycle and further that control voltage 53, is zero, full demagnetizing voltage will be applied to Winding 11 through rectifier 16. This results in the magnetization level of core fill being reset at a predetermined given level below saturation. In the following half-cycle, demagnetizing voltage is blocked from winding 1 by rectifier 16 while magnetizing voltage is applied to winding .2, magnetizing current flowing either through the load impedance and rectifier 17 or through bypass resistance 21 and rectifier 22. Since the full and equal time-integral of magnetizing and demagnetizing voltages have been applied, in the magnetizing half-cycle the magnetization level of the core is raised from the given level below saturation just to the saturation level without the flow of saturation current. While a portion of themagnetizing current may flow through impedance 1-8, the value of this current is very small, being limited to the width of the hysteresis curve of core 18, and is assumed of negligible effect on the output impedance.

When control voltage E is not zero. but some fractional part of demagnetizing voltage then in the reset halfcycle the full time-integral of demagnetizing voltage is not available. The effective resetting voltage now available for demagnetizing core 1% is e 1 to tire difierence voltage (E -E whereby the mag ization level of core 1b is not shifted to the given level referred to above, but generally to *1 intermediate level in accordance with the reduced effectiveness of the demagnetizing voltage. Obviously, should the difference oltage be zero the magnetization level will not be shifted from the saturation level but will remain thereat throughout the demagnetizing half-cycle. in the next half-cycle, being a magnetizing half-cycle, with the core ini ally set at an intermediate level the full time-integral of magnetizing voltage is no longer required to cause saturation of the core. Thus, application of magnetizing voltage E to winding 12 first causes saturation of the core in the magnetizing period, as described, resulting in disappearance of the reactive voltage across winding 12. For the remainder of the magnetizing half-cycle, voltage E is applied directly to output impedance 18 and output or saturation current fiows in the circuit including source E winding 12, rectifier 17 and load impedance 18. Varying the magnitude of control voltage E the instant in the magnetizing half-cycle at which core saturation is effectcd, being the initiation of the load current phase, is likewise varied, whereby regulation of the amount of power supplied to the load is achieved.

To maintain the amount of power delivered to load 18 at the desired level, as determined by the setting of control voltage E the instant in the magnetizing half-cycle at which core 10 saturates must be absolutely controlled by voltage E and uninfiuenced by the characteristics of load impedance 18. In the absence of the bypass circuit the deleterious effect on the control of the amplifier by capacitive reactance of load 18 may best be illustrated by analyzing the amplifier action in the magnetizing phase of the second or magnetizing half-cycle of operation. Should there be a charge remaining on condenser 19 in the magnetizing period, the resultant unidirectional voltage existing across the load impedance subtracts directly from the magnetizing voltage applicable to winding '12, hence, the effective voltage applicable to the winding is correspondingly reduced. inasmuch as the full value of voltage E is no longer applied to winding 12, the instant at which core saturation occurs becomes indefinite since the time-integral of magnetizing voltage, which determines the time involved in shifting the core magnetization level a given amount, is partially dependent upon the charge on condenser 15*. The addition of the load impedance bypassing circuit, however, permits the proper magnetizing action to occur as has been described.

Rectifier 22 is shown in the figure in series with resistance 21 in the bypass circuit. Since the function of this rectifier is to block the application of voltage E, to winding 12 through the bypass circuit during demagnetizing half-cycles, it is to be understood that the position of this rectifier is not limited to that shown. Alternatively, rectifier 22 may be connected at any point in the circuit path including source E winding 12 and resistance 21.

Although the specific embodiment shown and described herein is preferred many modifications and variations may be made by those skilled in the art without departing from the spirit of the present invention which is not to be limited except insofar as necessary by the scope of the disclosure.

The invention described herein may be manufactured and used by or for the Government of the United'States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

In a' magnetic amplifier for controlling the application of an alternating voltage to a load, a saturable magnetic core, a series load circuit coupled to said core including an alternating voltage source, a load impedance, a load winding on said core, a unilateral impedance. said unilateral impedance poled to provide a magnetizing voltage to said load winding during odd half cycles of the alternating voltage whereby said core is driven toward saturation, a Series control circuit coupled to said core including the alternating voltage source, a control winding, a unilateral impedance, said unilateral impedance poled to provide a demagnetizing voltage to said control winding during even half cycles of the alternating voltage whereby said core is deinagnetized, a bypass unilateral impedance including a serially connected resistance and rectifier connected in parallel with said first mentioned unilateral impedance and said load impedance to provide a magnetizing current path independent of. said load impedance, said rectifier poled to provide current fiow during the even half cycles of said alternating voltage.

(References on following page) References Cited in the file of this patent OTHER REFERENCES UNITED STATES PATENTS Publication, AIEE Technical Paper, 51-217 "On the Mechanics of Magnetic Amplifier Operation by Ramey, 11475-997 Hoyt 4, 1923 Fig. 16, pages 19-23, May 2, 1951. 2,509,738 Lord May 30, 1950 5 Vickers Publication Bulletin 20A (copyright 1950),

page 9, 2nd column, line 12 on and Fig. 16. 

